1. Field
The present invention relates to a data transmission device and a data transmission method to be used for carrying out data transmission to and from each of a plurality of user terminals in order to perform video conferencing.
2. Description of the Related Art
Recently, because of progress in network and information technologies, deployment of video conferencing systems (also referred to as TV conferencing systems) are coming into practical use. A video conferencing system is used for connecting a plurality of user terminals to one another so that image information and voice information are sent and received among the plurality of user terminals.
A known exemplary video conferencing system operates to receive and redistribute images from and to all participants of the conference (see, for example, JP-A-10-126757).
In the system described in JP-A-10-126757, a picture including images (moving or static) of N conference participants is displayed on a display of each of the terminals. Further, in order to reduce a quantity of data to be transferred, only a speaker is displayed by way of a dynamic or moving image while the rest of the conference participants are displayed by way of static images.
Recently, along with the prevalence of mobile terminals such as mobile phones and PDAs (Personal Digital Assistants), there is an increasing demand for a system which enables participation in the video conference from remote locations.
However, the size of the display (and most importantly, the display resolution) of the mobile terminals such as the mobile phone and the PDA is very small as compared with the size and resolution of personal computers and video conference-dedicated terminals. Therefore, when the images of all the conference participants are displayed on the display of the mobile terminal, the visibility of each of the images of the conference participants is considerably deteriorated.